Continuously slipping magnetic clutch



June 11, 1963 T. A. KRAMER ETAL 3,092,934

commuousu SLIPPING MAGNETIC CLUTCH Filed May 26, 1961 2 Sheets-Sheet 1 s l' ll-"llllllllnlllll'lllllll'll'l'lllll hm QM INVENTORfi. 77/500025 A. ran e MIA/APO 4 (fay/r2- By Apr m? 77/014 iffaP/f/flfs.

n 1963 1-. A. KRAMER ETAL 3,092,984

CONTINUOUSLY SLIPPING MAGNETIC CLUTCH 2 Sheets-Sheet 2 Filed May 26, 1961 w l t% I TO 77/500496 awln 5/71/07 By APT/9MP THO/W United States Patent 3,092,984 CONTINUOUSLY SLIPPING MAGNETIC CLUTCH Theodore A. Kramer, Los Angeles, Minard A. Leavitt, Playa Del Rey, and Arthur Thom, Inglewood, Calif., assiguors to Telautograph Corporation, Los Angeles,

Calif., a corporation of Virginia Filed May 26, 1961, Ser. No. 113,002 11 Claims. (CI. 6430) This invention relates to electro-mechanical clutch construction and, more particularly, to an improved continuously slipping magnetic clutch design.

In many electro-mechanical systems, such as telescribing systems, it is desired to selectively control the movement of a mechanical member in response to an electrical control signal. In particular, in telescribing systems it is desired to selectively control the movement of a writing implement over a writing surface to accurately reproduce written information represented by an electrical control signal. Generally, to accomplish this, the electrical control signal is applied to a transducer arrangement which converts the control signal into mechanical energy, the mechanical energy in turn being utilized to directly control the movement of the writing implement. In providing such mechanical control, it is desired that the transducer arrangement rapidly and smoothly operate in response to changes in the magnitude of the applied control signal to accurately position the Writing implement.

Generally, in the past transducer arrangements for providing this control have include a controllable motor drive having its output coupled to a linkage arrangement the motion of which provides positioning of the writing implement. In such prior transducer arrangements to selectively position the linkage, the rotational output of the motor drive is directly controlled by a control signal applied to the motor drive. To position the writing implement in response to movement of the linkage arrangement, it is necessary that the linkage arrangement be capable of rapid acceleration and deceleration. Due to the acceleration and deceleration placed on the linkage arrangement as well as the general requirement that the writing implement produce a permanent visual trace on a writing surface, it is generally necessary that the linkage arrangement be of a rugged design, having a substantial mass. Due to the inherent inertia of such a linkage mass, an extremely high torque requirement is placed upon the motor drive in positioning the writing implement. This high torque requirement increases wear of the motor drive and also increases the overall costs in the motor control circuitry.

To overcome the above disadvantages of prior telescribing arrangements as well as to provide a telescriber which will reproduce written information with an approved accuracy, a novel telescriber system has been proposed. This new telescribing system is described in the eo-pending patent application, Serial No. 58,455, filed September 26, 1960, now Patent No. 3,046,336 and assigned to the same assignee as the present application. As described therein, it is contemplated that the continuous rotational output of a motor drive be selectively sampled to position a writing implement over a writing surface. In particular, it is contemplated that the means for sampling rotational movement include a magnetic clutch arrangement which operates in response to control signals to selectively couple rotational motion from the motor drive to position the writing implement. Accordingly, since the motor drive of this telescribed system continuously rotates to selectively position the writing implement, the disadvantages associated with the high instantaneous torque requirement placed upon the motor drive by the prior art teles-criber arrangements is substantially ovecome.

'ice

In attempting to provide the desired selective positioning control for the new telescriber system, however, it was found that the commercially available magnetic clutches did not provide for completely satisfactory operation. Specifically, to provide the desired position-control it is necessary that the clutches be capable of developing a torque output which varies directly as a function of the current signal used to energize the clutches. Further, to accurately sample the rotational output of the motor drive to produce such a torque output it is necessary that the magnetic clutch provide a degree of coupling between the rotational output of the motor drive and its associated driven member which is instantaneously variable as a function of the magnitude of the current applied to energize the clutch.

In addition, the clutches are operated in a continuous slip condition in which the friction surfaces are always in contact but only seldom fully engaged with no slip. As a result, unique problems in minimizing wear and retaining the same control characteristics over a long period of use are encountered in providing a suitable clutch for operation in such a telescriber unit.

In view of the above, the present invention provides an improved magnetic clutch capable of operating under continuous slip conditions without undue wear and without substantial change in its torque charcteristics. In particular the clutch provides a torque output which varies directly with changes in the control current utilized to energize the clutch. To accomplish this, the present invention provides a continuously slipping magnetic clutch in which the degree of coupling between its drive and driven member varies directly as a function of the magnitude of a current signal which is utilized to energize the magnetic clutch.

Briefly, to provide such a controlled torque output, the present invention contemplates a clutch design wherein a drive disc of magnetic material having an annular facing of hard non-magnetic material is fixedly coupled to rotate with a drive shaft. To provide a controllable torque output for the clutch, a drum of magnetic material is mounted for free rotation around the drive shaft. Disposed within the drum is an annular slot, which divides one radial face of the drum into inner and outer radial surfaces, the outer radial surface having a facing of soft non-magnetic material which engages the hard facing of the disc. In particular, the drum is so positioned on the drive shaft that the hard facing of the disc and the soft facing of the outer radial surface of the drum form wear surfaces which are continually in slipping friction contact and such that an air gap is maintained between the inner radial surface of the drum and the drive disc.

To provide means for energizing the clutch, a coil-bo-bbin assembly is mounted within the annular slot which when energized by a current signal generates a magnetic field in the drum which extends across the air gap through the drive disc and hence back to the drum. Due to the particular flux path provided by the present invention this magnetic field attracts the drum to the drive disc such that the friction force between the wear surfaces is varied directly with the magnitude of current applied to energize the coil assembly. Accordingly the degree of coupling between the wear surfaces is varied directly with changes in the control current which in turn directly varies the torque output developed by the drum.

A more complete understanding of the above as well as other features of the present invention may be had by reference to the following detailed description when considered with the drawings, in which:

FIG. 1 is a diagrammatic representation of a telescriber system to which the present invention is particularly adaptable;

FIG. 2 is a block circuit diagram of the electrical con 3 trol system for the telescriber system depicted in FIG. 1;

FIG. 3 is a cross sectional view of the magnetic clutch in accordance with the present invention; and,

FIG. 4 is a sectional side view of the present invention, a cross section of which is illustrated in FIG. 3.

Referring to FIG. 1, there is represented a telescriber system to which the magnetic clutch design of the present invention may be particularly adapted. The telescriber system is represented by the dotted line rectangle 10. As illustrated, the telescriber system includes a stylus arrangement 12 which is positioned over a writing surface 14. As shown, the stylus arrangement 12 is coupled to a carriage 16 which in turn is mounted for lateral movement along a bridge assembly 18. The bridge assembly 18 is in turn positioned on parallel guide members 17 and 19, which are attached to the frame of the telescriber assembly.

To produce a visual trace on the writing surface 14, movement is imparted to the bridge assembly 18 and the carriage 16 from a motor drive 20' through a special cable arrangement which is coupled to be driven from a magnetic clutch assembly. In particular, to provide the desired controlled movement of the stylus 12, rotational motion developed by the motor drive 20 is coupled to a drive shaft 22 by a worm gear arrangement represented at 24. The rotational movement of the drive shaft 22 is then selectively sampled by four magnetic clutches 26, 28, and 32 which are mounted in pairs at either end of the drive shaft 22. The rotational motion sampled by the clutches is then utilized to position the stylus member 12 through the associated cable drive.

Specifically, as represented in FIGURE 1, at one end of the drive shaft 22 there are positioned magnetic clutches 26 and 28, magnetic clutch 26 including a drive member 34 fixedly coupled to rotate with the drive shaft 22 and a cylindrical driven member 36 which is mounted for free rotation around the drive shaft 22. Similarly, the magnetic clutch 28 includes a drive member 38 which is fixedly coupled to the drive shaft 22 and a cylindrical driven member 40 mounted for free rotation around the drive shaft 26. In like manner, the pair of clutches 30 and 32 are coupled at the other end of the drive shaft 22 and include, respectively, drive members 40 and 42 and cylindrical driven members 44 and 46.

To provide means for energizing the clutch assemblies such that each clutch may independently sample rotational movement of the drive shaft 22, electromagnet means (not shown) is located within each of the driven members. To then actuate a particular clutch, a current signal is applied at one of the input terminals 48, 50, 52 or 54. This current causes the electromagnet associated with the particular clutch to energize, thereby coupling the associated driven member to the drive shaft through its associated drive member. More particularly, since it is contemplated by the present invention that the magnetic clutches are continuously slipping clutches of the type to be desribed in connection with FIGURES 3 and 4, an increase in electrical current applied to a clutch increases the friction force between its driven member and its associated drive member. This in turn reduces the slippage between the drive and driven members causing the driven member to rotate with the drive shaft. In a like manner, a reduction in the applied current causes a reduction in the friction between the driven member and its associated drive member, thereby increasing the slippage therebetween. As will be described in detail, this selective operation on each magnetic clutch provides means for selectively positioning the stylus arrangement 12 at any point on the writing surface 14.

As previously mentioned, by a special cable arrangement the four magnetic clutches are utilized to control the movement of the carriage 16 from the motor drive 20. This special cable arrangement is described in detail in the co-pending patent application, Serial No. 58,455, filed September 26, 1960, now Patent No. 3,046,336 and assigned to the same assignee as the present invention. As therein described, the cable arrangement includes two lengths of cable 58 and 60, both of which are anchored at two ends of the carriage 16. The length of cable indicated at 58 extends from the left-hand side of the carriage 16 around a pulley member 62 which is mounted on the bridge assembly 18, over a pulley 64 to a cylindrical driven member 36 of the magnetic clutch 26. As illustrated, the cable length 58 is wrapped several times around the driven member 36, then passes around a pulley 66 to a potentiometer represented at 68. The cable length 58 after making a revolution around the potentiometer 68 passes over a pulley 70 to the cylindrical driven member 46 of the magnetic clutch 30. As illustrated, the cable length 58 makes a series of loops around the driven member 46 and thence over a pulley 72 which is mounted upon the bridge assembly 18, to the carriage 16 where it is fixedly attached.

A like member, cable length 60, extends from the lefthand side of the carriage 16 over a pulley 74 which is mounted upon the bridge assembly 18, to the cylindrical driven member 40 of the magnetic clutch 28. As illustrated, the cable length 60 makes a series of wraps around the driven member 40 and hence over a pulley 76 to a potentiometer arrangement represented at 78. After making a revolution around the potentiometer 78, the cable length 60 passes over a pulley 80 and hence to the cylindrical driven member 48 of the magnetic clutch 32. As illustrated, the cable length 60 makes a series of turns around the driven member 48 and then passes over a pulley 82, to a pulley 84, which is mounted upon bridge assembly 18, to the right-hand side of the carriage 16 where it is fixedly attached.

Each of the magnetic clutches is controlled by a current signal applied to one of the terminals 50, 52, 54 or 56. In particular, this control signal is derived from a comparison circuit. As represented in FIGURE 2, the rotational positions of the clutches 26 and 30 determine the magnitude of the signal developed by the potentiometer 68. This in turn represents the particular position of the stylus arrangement 12 over the writing surface 14. A signal representing like positional information is applied to terminal 86. This signal may have been generated at a transmitting location remote to the telescribing system represented in FIGURE 1 by an operator moving a mechanical stylus arrangement over a writing surface. As represented in FIGURE 2 the signal generated by the potentiometer 68 and the signal received at terminal 86 are applied to a differential amplifier 88. These signals are compared by the differential amplifier 88 which generates an output signal proportional to the difference between the input signals. The output signal developed by the differential amplifier 88 is applied to an amplifier 89 which controls the current applied to the terminal 50 of the magnetic clutch 26 and to an inverter circuit represented at 90. Inverter 90 inverts the magnitude of the output signal produced by the differential amplifier 88 and applies this inverted signal to an amplifier 91 which controls the current applied to the terminal 54- of the magnetic clutch 30. Thus in responser to the output of the differential amplifier 88 one of the magnetic clutches 26 and 30 is energized such that slippage between its driven and drive members is reduced to cause its drive member to rotate with the shaft 22 while the slippage between the drive and driven members of the other magnetic clutch is increased. Accordingly the length of cable 58 is caused to move in a direction determined by the rotation of the drive shaft 22 and a particular driven member associated with the clutches 26 and 30 which is caused to rotate with the drive shaft 22.

Although not specifically shown, a like control arrangement is included for the magnetic clutches 28 and 32. These clutches derive their control from the potentiometer arrangement represented at 78. Thus the length of cable 60 is caused to move in a direction determined by the rotation of the drive shaft 22 and the particular driven member associated with the clutches 28 and 32 which is caused to rotate with the shaft 22.

Accordingly from the above it appears that due to the particular clutch and cable arrangement, energizing one of the four clutches produces equal movement of the bridge and carriage assembly. This results in movement of the stylus member along one or the other of two mutually perpendicular 45 diagonal axes, the direction of the movement along either of these axes being determined by which of the two clutches associated with a particular one of the two cable lengths is energized.

If two clutches are simultaneously energized by cur rents of equal magnitude, the two clutches being associated respectively with each of the two cable sections, movement of the stylus arrangement will be either along a or X-axis or along a 90 or Y-axis. Again, the direction of the movement is determined by the combination of two clutches selectively energized. Thus by varying the magnitude of the current applied to each magnetic clutch, to directly vary the degree by which each clutch samples rotational movement from the drive shaft 22, movement of the stylus arrangement 12 can be selectively controlled in any direction over the writing surface 14. a

From the above description it appears that to provide accurate positioning of the stylus arrangement, the magnitude of the control signals should be directly related to the desired position of the stylus arrangement. Further, the rotational torque output for each of the clutches should vary directly with changes in magnitude of the control current applied to the clutches. Still further, it should be realized that to provide the desired position control the magnetic clutches should be responsive to rapid changes in the magnitude of the control currents applied thereto. In particular, the clutch construction should provide a degree of coupling between the drive shaft 22 and its associated cable arrangement which varies directly with changes in the current applied to the magnetic clutch. A magnetic clutch providing such a torque output is represented in cross section in FIGURE 3.

As illustrated in FIGURE 3, the magnetic clutch of the present invention includes a drive disc represented at 92 which is fixedly pinned at 94 to rotate with a drive shaft 96. As represented, the drive disc 92 includes an inner radial portion 98 of magnetic material and outer annular portion 100 of non-magnetic material having a facing 102 of hard non-magnetic Wear material.

To provide the controllable torque output for the clutch of the present invention a drum of magnetic material 104 is mounted for free rotation around the drive shaft 96 by a bearing arrangement represented in cross section at 106. As illustrated, the drum 104 includes forward and rear radical faces represented at 108 and 110. As shown the radial face 108 of the drum 104 includes an annular slot 112 which divides the radial face 108 into inner and outer radial surfaces 114 and 116. In particular, the outer radial surface 116 includes a facing 118 of a soft non-magnetic wear material which together with the outer radial surface 116 extends beyond the inner radial surface 114 in a plane normal to the radial face 108. As is further illustrated in FIGURE 3 the radial face 110 is also divided into inner and outer radial surfaces by an annular slot 119 which is included to reduce the mass of the drum 104.

As represeented in FIGURE 3 the drum 104 is so positioned on the drive shaft 96 that the facing of soft material 118 is in continuous slipping contact with the facing of hard material 102. Further, due to the aforementioned cross section of the inner and outer radial surfaces of the drum 104 an air gap represented at 120 is created between the inner radial surface 114 of the drum 104 and the inner radial portion 98 of the drive disc 92.

As previously mentioned it is desired that the clutch of the present invention develop a torque output which varies directly with the magnitude of the applied control current. To accomplish this it is necessary that the degree of coupling between the drive disc 92 and the drum 104 be directly controllable as a function of control current. To provide such coupling control it was found that a continuous slipping contact between the drive disc 92 and the drum 104 was necessary. In providing the desired slipping contact it was further discovered that a combination of hard and soft wear surfaces provided superior controlled coupling. In particular it was found that a hard wear surface of beryllium copper and a soft wear surface of Rulon (a trade name for Teflon with a lead derivative) provided a long wearing friction contact which with the clutch deenergized acted as a low friction bearing coupling. Further it was found that with the clutch energized the beryllium copper-Rulon combination provided a degree of coupling which was directly controllable as a function of the force between the drive disc 92 and the drum 104. Accordingly in a preferred form of the present invention the facing of hard material 102 is composed of beryllium copper while the facing of soft material 118 is composed of Rulon.

To selectively control the force between the drive disc 92 and the drum 104 such that the degree of coupling therebetween may be directly varied, means are provided for generating a magnetic field across the air gap 120. In particular, the magnetic field attracts the drum 104 to the drive disc 92 with a force which is a function of the magnitude of the control current utilized to generate the magnetic field. In the form of the present invention represented in FIGURE 3, the means for generating the desired magnetic field takes the form of a coil-bobbin assembly 122 positioned within the annular slot 112 for rotation with the drum 104. As represented, coil-bobbin assembly 122 is energized by current flowing through a conductor 124 which is connected to the coil-bobbin assembly 122 through a hole 125 in the drum 104. In particular, a current applied to the coil-bobbin assembly 122 generates a magnetic field having a flux path represented by the dashed line 127 which extends Within the drum 104, around the slot 112, across the air gap 120. into the inner radial portion 98 of the drive disc 92 to the outer radial surface 116 of the drum 104.

As previously mentioned, to provide the desired accuracy of current control, the clutch design should be responsive to rapid changes in the magnitude of the control current. In addition to the continuous slipping contact between the drive and driven members of the clutch, this requires that the magnetic materials of the clutch which form the flux path for the controlling magnetic field be of a soft magnetic material having a low flux remanence. In providing such construction, it was found that for the design of the present invention the low carbon steel Relay No. 5 (a trade name) provided a superior response. Thus, in a preferred form of the present invention, the inner portion 98 of the drive disc 92 and the drum 104 are composed of Relay No. 5.

Accordingly, it has been found that by utilizing the particular hard and soft wear surface combination as well as the above described flux path configuration as current applied to the conductor 124 is varied, the coupling force between the facings of wear material varies to cause the drum 104, with a substantially constant load, to rotate with an angular velocity determined by the degree of coupling between the faces. This in turn produces a torque output for the drum 104 which varies directly with the magnitude of the applied current.

To provide means for coupling a torque driven load, such as the cable arrangement of FIGURE 1, to the drum 104, a disc 126 of non-magnetic material such as a plastic is positioned adjacent to the rear face of the drum 104. As illustrated in FIGURE 3, the disc 126 includes a flange 128 extending from the radial extremity of the disc 126. As illustrated, the flange 128 is positioned in a cable arrangement represented in FIG. 1 to the drum .the collar 138, a disc 104 thereby substantially enclosing the drum 104. In particular as represented to provide means for coupling a cable arrangement represented in FIG. 1 to the drum 104, the flange 1218 includes a series of ridges represented at 132 and rims 134 and 136.

As is further illustrated in FIG. 3, the disc of nonmagnetic material 126 includes a collar 138 extending around a hole 140, which, as shown, is centrally disposed within the disc 126 to receive the drive shaft 96. As illustrated in FIGURES 3 and 4, the conductor 124 is secured in a spiral wrap around the collar 138.

In order to maintain this spiral wrap while the coilbobbin assembly 122 is rotating with the drum 104, a spacer disc 142 is mounted around the collar 138 in pressure contact with the rear surface of the disc 126. In particular, it is the spacer 142 which provides means for guiding the conductor 124 to the coil-bobbin assembly 122. To accomplish this, the disc 142 includes a slot 144 which extends radially from the collar 138. Accordingly, the conductor 124 extends from its spiral wrap at the collar 138 through the slot 144 through the disc 126 to the coil-bobbin assembly 122.

To further maintain the spiral wrap of the conductor 124, a circular spring clip 146 is positioned around the collar 138. In particular, as shown in FIGURE 4, one end of the spring clip 146 is positioned in a slot 148 which extends longitudinally in the collar 138. The spring clip 146 then extends around the collar 138 subtending a first turn of the conductor 124. In this manner, the spring clip 146 fixedly secures the first wind of the conductor 124 to the collar 138.

To maintain the remainder of the spiral wrap around 150- of non-conducting material such as plastic is positioned around the end of the collar 138. Accordingly, as the drum 104 is caused to rotate, the conductor 124 winds or unwinds depending upon the direction of rotation of the drum 104. Further, due to the combination of discs 142 and 150 and the spring clip arrangement 146, the conductor 124 is maintained in a spiral wrap around the collar 138.

The conductor wrap arrangement described above comprises a feature of the present invention. In the past to provide means for energizing a coil arrangement which rotated as a portion of a driven member, it was necessary to include a slip ring assembly in combination with the driven member. Such slip ring assemblies have the disadvantage of occupying an appreciable amount of space. Further, due to the friction contact of the assembly they provided an inefficient means of transmitting electrical signals to the coil of a driven member. By use of the present invention, however, both of these disadvantages are overcome.

What is claimed is:

l. A continuously slipping magnetic clutch comprising: a drive disc fixedly mounted for rotation with a drive shaft, said drive disc having forward and rear faces and including an inner radial portion of magnetic material and an outer annular portion of non-magnetic material; a drum of magnetic material mounted for free rotation around said drive shaft adjacent to said drive disc, said drum having a forward and a rear surface, said forward surface including an annular slot dividing said forward surface into inner and outer planar surfaces, said outer planar surface projecting beyond the plane of said inner planar surface; a first facing of wear material impressed on said outer annular portion of said disc flush with the rear face of said drive disc; a second facing of wear material impressed on said outer planar surface of said drum, a one on said facings comprising a hard wear material and the other comprising a soft wear material, said first and second facings being positioned in continuous slipping friction contact to cause said drum to tend to rotate with said drive disc, the contacting wear materials maintaining an air gap between said inner planar surface of said drum and said rear face of said drive disc; a bobbin arrangement mounted within said annular slot for rotation with said drum; an electrical coil wound around said bobbin for generating a magnetic field through said drum and drive disc when said coil is energized by an electric current; a driven disc of nonmagnetic material having forward and rear surfaces, said driven disc including an annular flange at a radial extremity of its forward surface and a collar having a longitudinal slot therein surrounding a hole which is centrally disposed in said driven disc to receive said drive shaft, said flange being positioned in pressure contact with an outer surface of said drum to cause said driven disc to rotate with said drum; a spacer disc mounted on said collar in pressure contact with the rear surface of said driven disc, said spacer disc having a slot extending radially from said collar; a flexible conductor extending around said collar and through the radial slot; means for connecting said conductor to said coil to energize said coil in response to current signals applied to said conductor; a circular spring clip having one end positioned in said longitudial slot and extending around said collar to secure a first turn of said conductor around said collar; and means positioned around the end of said collar to maintain said conductor in a spiral wrap around said collar when said drum is rotated.

2. A continuously slipping magnetic clutch comprising: a drive disc fixedly mounted for rotation with a drive shaft, said drive disc having forward and rear faces and including an inner radial portion of magnetic material and an outer annular portion of nonrnagnetic material; a drum of magnetic material mounted for free rotation around said drive shaft adjacent to said drive disc, said drum having a forward and a rear surface, said forward surface including an annular slot dividing said forward surface into inner and outer planar surfaces, said outer planar surface projecting beyond the plane of said inner planar surface; a first facing of wear material impressed on said outer annular portion of said drive disc; a second facing of wear material impressed on said outer planar surface of said drum, a one of said facings comprising a hard wear material and the other comprising a soft wear material, said first and second facings being positioned in continuous slipping friction contact to tend to rotate said drum with said drive disc, the contacting wear materials maintaining an air gap between said inner radial surface of said drum and said rear face of said drive disc; a bobbin arrangement mounted within said annular slot; an electrical coil wound around said bobbin for generating a magnetic field through said drum and drive disc when said coil is energized by a current signal; a driven disc of non-magnetic material having forward and rear surfaces, said driven disc including an annular flange at a radial extremity of its forward surface and a collar surrounding a hole which is centrally disposed in said driven disc to receive said drive shaft, said flange being positioned in pressure contact with an outer surface of said drum to cause said driven disc to rotate with said drum; a flexible conductor wrapped in a loose spiral around said collar, one end of said conductor being connected to said coil of said bobbin and the other end connected to means for receiving a current signal to energize said coil to selectively vary the slipping friction between the contacting facings of wear material; and means for maintaining the spiral wrap of said conductor when said drum is rotated with said drive disc.

3. A continuously slipping magnetic clutch comprising: a drive disc fixedly mounted for rotation with a drive shaft, said drive disc having forward and rear faces and including an inner radial portion of magnetic material and an outer annular portion of non-magnetic material; a drum of magnetic material mounted for free rotation around said drive shaft, said drum having a forward and a rear surface, said forward surface including an annular slot dividing said forward surface into inner and outer planar surfaces, said outer planar surface projecting beyond the plane of said inner planar surface; a first facing of wear material impressed on said outer annular portion of said drive disc; a second facing of wear material impressed on said outer planar surface of said drum, a one of said facings comprising a hard wear material and the other facing comprising a soft wear material, said first and second facings being positioned in continuous slipping friction contact to tend to rotate said drum with said drive disc; a bobbin arrangement mounted within said annular slot; an electrical coil wound around said bobbin for generating a magnetic field through said drum and drive disc when said coil is energized by a current signal; a hollow drum of non-magnetic material surrounding said drum of magnetic material; and means for receiving a current signal to energize said coil to selectively vary the slipping friction between the first and second facings.

4. A continuously slipping magnetic clutch comprising: a drive member of magnetic material fixedly mounted for rotation with a drive shaft; a driven member including a drum of magnetic material mounted for free rotation around said drive shaft adjacent to said drive member, said drum having an annular slot disposed therein to divide said drum into inner and outer radial portions; a first annular facing of non-magnetic wear material impressed on said drive member; a second annular facing of non-magnetic wear material impressed on said outer radial portion of said drum, a one of said facings comprising a hard wear material and the other facing comprising a soft wear material, said first and second facings of wear material being in continuous slipping friction contact; a coil-bobbin assembly mounted within said annular slot; and means for applying a current signal to said coil-bobbin assembly to generate a magnetic field between said drive and driven members to vary the slipping friction between the first and second facings of wear material in a substantially direct proportion to the applied current.

5. A continuously slipping magnetic clutch as defined in claim 4 wherein said hard wear material is composed of beryllium copper and wherein said soft wear material is composed of Rulon.

6. A continuously slipping magnetic clutch comprising: a drive member of magnetic material rotated about its axis of rotation; a driven member of magnetic material mounted for free rotation relative to said drive member; a first facing of non-magnetic wear material impressed upon a portion of said drive member; a second facing of non-magnetic wear material impressed upon a portion of said driven member, a one of the facings comprising a hard wear material and the other facing comprising a soft wear material, said first and second wear surfaces being positioned in continuous slipping friction contact, the contacting wear materials maintaining an air gap between said drive and driven members; and means for initiating a variable magnetic field across said air gap to selectively control the slipping friction between the facings of wear material.

7. A continuously slipping magnetic clutch comprising: a drive member of magnetic material mounted for rotation with a drive shaft and including a first ring of nonmagnetic Wear material impressed on a radial surface of the drive member; a driven member of magnetic material mounted for free rotation around said drive shaft; a second ring of non-magnetic wear material disposed on said driven member, and positioned in continuous slipping friction contact with said first ring of wear material, the rings of wear material maintaining a low permeability gap between said driven member and said drive member; a coil assembly mounted on said driven member; a conductor connected to said coil assembly; means for maintaining said conductor in a spiral wrap around said drive shaft when said driven member rotates with said drive 10 member; means coupled to said conductor for applying a control current to said coil assembly to generate a variable magnetic field across the gap between the driven and drive members to vary the slipping friction between the rings of wear material; and means for coupling a driven load to said driven member.

8. A continuously slipping magnetic clutch comprising: a drive member of magnetic material mounted for rotation with a drive shaft and including a first ring of nonmagnetic wear material impressed on a radial surface; a drum of magnetic material mounted for free rotation around said drive shaft; a second ring of non-magnetic wear material disposed on said drum, one of said rings comprising a hard wear material and the other ring comprising a soft wear material, said first and second rings being positioned in continuous slipping friction contact, the rings of wear material maintaining a low permeability gap between said drum and said drive member; a coil assembly disposed within said drum for inducing a magnetic field across said gap; means coupled to said coil assembly for applying a control current to said coil assembly to vary the slipping friction between the rings of wear material; and means for coupling a driven load to said drum.

9. A continuously slipping magnetic clutch comprising: a drive member of magnetic material fixedly mounted for rotation with a drive shaft; an annular facing of hard nonmagnetic wear material impressed on said drive member; a driven member including a drum of magnetic material mounted for free rotation around said drive shaft, said drum having an annular slot disposed therein to divide said drum into inner and outer planar surfaces, said outer planar surface projecting beyond the plane of said inner planar surface; an annular facing of soft non-magnetic wear material impressed on said outer planar surface of said drum; said facing of soft wear material being positioned in continuous slipping friction contact with said facing of hard wear material, the contacting wear surfaces maintaining an air gap between said inner planar surface of said drum and said drive member; and means for initiating a variable magnetic field across said air gap to selectively control the normal force between the facings of wear material.

10. A continuously slipping magnetic clutch comprising: a drive member of magnetic material mounted for rotation with a drive shaft; a first annular facing of nonmagnetic wear material impressed on said drive member; a. driven member including a drum of magnetic material mounted for free rotation around said drive shaft, said drum having an annular slot disposed therein to divide said drum into inner and outer planar surfaces, said outer planar surface projecting beyond the plane of said inner planar surface; a second annular facing of non-magnetic wear material impressed on said outer radial surface of said drum, one of said facings comprising a hard wear material and the other facing comprising a soft wear material, said first and second facings being positioned in continuous slipping friction contact to tend to rotate said drum with said drive member and to maintain an air gap between said inner planar surface and said drive member; and means mounted within said annular slot for initiating a variable magnetic field across said air gap to selectively control the normal force between the facings of wear material.

11. A continuously slipping magnetic clutch comprising: a drive disc fixedly mounted for rotation with a drive shaft, said drive disc having forward and rear faces and including an inner annular radial portion of magnetic material and an outer annular portion of non-magnetic material; a drum of magnetic material mounted for free rotation around said drive shaft, said drum having a forward and a rear surface, said forward surface including an annular slot dividing said forward surface into inner and outer planar surfaces, said outer planar surface projecting beyond the plane of said inner planar surface; a

11 first facing of wear material impressed on said outer annular portion of said drive disc; a second facing of wear material impressed on said outer planar surface of said drum, one of said facings comprising a hard wear material and the other facing comprising a soft wear 5 material, said first and second facings being positioned in continuous slipping friction contact to tend to rotate said drum with said drive disc and to maintain an air gap between said inner planar surface and the inner radial portion of said drive disc; and means within said annular m slot for generating a magnetic field through said drum and drive disc to selectively vary the slipping friction contact between the first and second facings.

References Cited in the file of this patent UNITED STATES PATENTS 828,647 Gibbs Aug. 14, 1906 2,039,714 Fuller May 5, 1936 2,214,901 Griffin Sept. 17, 1940 

1. A CONTINUOUSLY SLIPPING MAGNETIC CLUTCH COMPRISING: A DRIVE DISC FIXEDLY MOUNTED FOR ROTATION WITH A DRIVE SHAFT, SAID DRIVE DISC HAVING FORWARD AND REAR FACES AND INCLUDING AN INNER RADIAL PORTION OF MAGNETIC MATERIAL AND AN OUTER ANNULAR PORTION OF NON-MAGNETIC MATERIAL; A DRUM OF MAGNETIC MATERIAL MOUNTED FOR FREE ROTATION AROUND SAID DRIVE SHAFT ADJACENT TO SAID DRIVE DISC, SAID DRUM HAVING A FORWARD AND A REAR SURFACE, SAID FORWARD SURFACE INCLUDING AN ANNULAR SLOT DIVIDING SAID FORWARD SURFACE INTO INNER AND OUTER PLANAR SURFACES, SAID OUTER PLANAR SURFACE PROJECTING BEYOND THE PLANE OF SAID INNER PLANAR SURFACE; A FIRST FACING OF WEAR MATERIAL IMPRESSED ON SAID OUTER ANNULAR PORTION OF SAID DISC FLUSH WITH THE REAR FACE OF SAID DRIVE DISC; A SECOND FACING OF WEAR MATERIAL IMPRESSED ON SAID OUTER PLANAR SURFACE OF SAID DRUM, A ONE ON SAID FACINGS COMPRISING A HARD WEAR MATERIAL AND THE OTHER COMPRISING A SOFT WEAR MATERIAL, SAID FIRST AND SECOND FACINGS BEING POSITIONED IN CONTINUOUS SLIPPING FRICTION CONTACT TO CAUSE SAID DRUM TO TEND TO ROTATE WITH SAID DRIVE DISC, THE CONTACTING WEAR MATERIALS MAINTAINING AN AIR GAP BETWEEN SAID INNER PLANAR SURFACE OF SAID DRUM AND SAID REAR FACE OF SAID DRIVE DISC; A BOBBIN ARRANGEMENT MOUNTED WITHIN SAID ANNULAR SLOT FOR ROTATION WITH SAID DRUM; AN ELECTRICAL COIL WOUND AROUND SAID BOBBIN FOR GENERATING A MAGNETIC FIELD THROUGH SAID DRUM AND DRIVE DISC WHEN SAID COIL IS ENGERIZED BY AN ELECTRIC CURRENT; A DRIVEN DISC OF NONMAGNETIC MATERIAL HAVING FORWARD AND REAR SURFACES, SAID DRIVEN DISC INCLUDING AN ANNULAR FLANGE AT A RADIAL EXTREMITY OF ITS FORWARD SURFACE AND A COLLAR HAVING A LONGITUDINAL SLOT THEREIN SURROUNDING A HOLE WHICH IS CENTRALLY DISPOSED IN SAID DRIVEN DISC TO RECEIVE SAID DRIVE SHAFT, SAID FLANGE BEING POSITIONED IN PRESSURE CONTACT WITH AN OUTER SURFACE OF SAID DRUM TO CAUSE SAID DRIVEN DISC TO ROTATE WITH SAID DRUM; A SPACER DISC MOUNTED ON SAID COLLAR IN PRESSURE CONTACT WITH THE REAR SURFACE OF SAID DRIVEN DISC, SAID SPACER DISC HAVING A SLOT EXTENDING RADIALLY FROM SAID COLLAR; A FLEXIBLE CONDUCTOR EXTENDING AROUND SAID COLLAR AND THROUGH THE RADIAL SLOT; MEANS FOR CONNECTING SAID CONDUCTOR TO SAID COIL TO ENERGIZE SAID COIL IN RESPONSE TO CURRENT SIGNALS APPLIED TO SAID CONDUCTOR; A CIRCULAR SPRING CLIP HAVING ONE END POSITIONED IN SAID LONGITUDIAL SLOT AND EXTENDING AROUND SAID COLLAR TO SECURE A FIRST TURN OF SAID CONDUCTOR AROUND SAID COLLAR; AND MEANS POSITIONED AROUND THE END OF SAID COLLAR TO MAINTAIN SAID CONDUCTOR IN A SPIRAL WRAP AROUND SAID COLLAR WHEN SAID DRUM IS ROTATED. 